Field of the Invention
The present invention relates to converter technologies in the field of power electronics, and more particularly to a voltage-source multi-level converter, a direct-current (DC) power transmission system, and a fault processing method and device.
Description of Related Art
A voltage-source multi-level converter is a novel type of converter applicable to high voltage scenarios that attracts much concern in recent years, where sub-modules are cascaded, and states of the sub-modules are respectively controlled, such that an alternating-current (AC) voltage output by the converter may be approximate to a sine wave, thereby reducing the harmonic content of the output voltage. The voltage-source multi-level converter solves a voltage equalizing problem of series-connected parts of a voltage-source two-level converter.
With some voltage-source multi-level converters in the related art, when a DC line has a fault, an AC network may provide a fault current to a fault point, causing an over-current at a DC side. A method for solving the foregoing problem is to install a hybrid high-voltage direct-current (HVDC) circuit breaker at the DC side of the converter, so as to block a path for the AC network to provide the fault current to the fault point, thereby preventing the AC network from providing the fault current to the fault point when the DC line has the fault, and avoiding the over-current at the DC side.
However, a solution in the related art for solving the problem of an over-current at a DC side caused by providing a fault current to a fault point when a DC line has a fault in a voltage-source multi-level converter involves a complex implementation process and high costs. Therefore, how to use a simple and economical manner to solve the problem of an over-current at a DC side caused by providing a fault current to a fault point when a DC line has a fault in a voltage-source multi-level converter is of great significance.